Capsizable Catamaran

Discussion in 'Boat Design' started by PlaningWheel, May 23, 2012.

  1. PlaningWheel
    Joined: Nov 2010
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    PlaningWheel Junior Member

    I've seen many designs to right a cat after a capsize. They all involved flooding 1 hull or the ends of both hulls plus mast floats and counter weights. None of them were very practical and none worked in full scale tests.
    So don't right the boat instead pivot the mast 180 degrees and reverse the rudders.
    The hull design is taken from an old day sailing cat called the Sizzler:
    http://www.thebeachcats.com/news/116/the-sizzler-catamaran,-aluminum-beachcat/
    In this case the boat is somewhat bigger (52') and the hulls are connected by two 8' wide by 3.5' tall box beams with usable space inside.
    Upright it has about 5' clearance between the keel and the bottom of the box beams.
    Inverted it has about 3.5'.
    An "A" frame can be stowed under the deck to use when rerigging the mast.
    All tanks should be duplicated in the floor and ceiling with connecting pipes.
    Works best with a pivoting toilet!

    Colin
    http://www.ww.xbug.ca
     

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  2. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Its been thought of many times before. It has never been built. I regard it as unworkable.
     
  3. PlaningWheel
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    PlaningWheel Junior Member

    I'd like to see one of the other ones that's been thought of before.
    Searching U.S. patents under "capsizable" I got the following:

    1) 6,073,569 Advantageous use of battery mass in electric watercraft
    2) 3,974,535 Boat hull with spherical dome

    The only ones I've seen all involved rotating the hulls?

    Colin
    http://www.ww.xbug.ca
     
  4. rwatson
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    rwatson Senior Member

    There have been at least two suggestions in the last 24 months on this very forum. If we had decent search facilities, I could look them up for you.

    I am not surprised there are no patents on the idea, as it is not practical.

    The weight penalties for duplicated floor soles and general "upsidedowness" alone would ruin the idea, let alone designs to let all gear operate on two horizons. Toilets are the least of your worries.
     
  5. PlaningWheel
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    PlaningWheel Junior Member

    I'm not suggesting that you carry on your cruise upside down. But you can limp to shore (perhaps with block and tackles replacing winches if they can not be relocated).

    Duplicating the tanks is not really required. You can dump your waste and fuel and just keep some water.
    In any case tankage should just be part of the mechanical structure to begin with.
    I don't think there's much of a weight penalty involved here.
    As far as rerigging at sea I guess you would wait for a calm day.

    I don't think that there are other designs on the forum that feature a pivoting rig.
    Or that combine a symmetrical hull design (1 mold for all 4 sides - or possibly 8 sections from 1 mold) and symmetrical box beams to hold them together (1 mold = 4 sections).
    Or that don't require re-righting the hulls after a capsize.

    Colin
    http://www.ww.xbug.ca
     
  6. rwatson
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    rwatson Senior Member

    Sigh ... all inventors find it hard to think that others could be as clever as themselves -

    For a start, read the thread "self righting motor trimaran", in particular post 26
    http://www.boatdesign.net/forums/boat-design/self-righting-motor-trimaran-30769.html

    Now, if you take the trouble to look through dozens of multihull capsize discussions, your concepts get bandied around from time to time.
     
  7. PlaningWheel
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    PlaningWheel Junior Member

    self righting motor trimaran

    Not the same at all.

    It's not a sail boat.

    So what if the center hull swivels 180 adding huge compromises and weight to the design.
    Swivel the motor/drive instead or better still don't bother with the idea to begin with.
    Read post 26 but you can't do it with a sailing tri.
    I first considered the idea 35 or so years ago (what to do about an ocean capsize).
    At the time the answer was to buy a monohull and sail slow in a hull that will sink like a stone if it is breached in any way.
    The cat I presented is I think a good compromise with a very light and strong structure that is easy to build.
    First inspired by the early Wharram cat designs. When he was going from V hulls to more rounded hull shapes.

    Colin
    http://www.ww.xbug.ca
     
  8. rwatson
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    rwatson Senior Member

    I didnt say it was the same - if you look at post 26 like I suggested, someone playfully suggests the upside down cat idea - one example of quite a few I have seen over the years I have been following the forums.
     
  9. bpw
    Joined: May 2012
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    bpw Senior Member

    That's a lot of compromises for something that happens very rarely.

    how do you walk around on those pointy decks?
     
  10. quequen
    Joined: Jul 2009
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    quequen Senior Member

    I worked on this idea a cup of years ago, for a handicaped, needy of adenaline friend. I thought I was the capsizable catamaran concept inventor!. It is rotomoulded in polietylene, cheap and strong. Spar rotates forwards pulled by a double-sided sheet and gets stoped by two spectra forestays. Helmsman chair rotates by gravity, no way to remain upside down. Rudders and daggerboards (not modeled) are reversible and just fall down by gravity to the right position. For share/sale with/to anyone having interest on building it :)
     

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  11. PlaningWheel
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    PlaningWheel Junior Member

    To bpw,
    You're probably right. Capsizing does appear to be a rare event nowadays. Perhaps in part because of satellite imaging?

    To quequen,
    You are showing a daysailer why not right it in the usual manner.
    Years ago I attached an aluminum tube "A" frame under a Hobbie tramp to give me extra leverage when I was sailing alone.

    Colin
    http://www.ww.xbug.ca
     
  12. quequen
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    quequen Senior Member

    Remember the guy on the chair can only move his hands.
    Spar is intendet to be very light, and a top zeppelin could avoid complete capsize making things easier.
     
  13. PlaningWheel
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    PlaningWheel Junior Member

    A Hobie 16 had 175 sq.ft. of sail. If I sailed it alone sitting on the windward rail it was all I could do to keep it upright in a light breeze.
    Sitting in the middle would not have worked at all.
    Even out on the trapeze wire it was very easy to flip without a second person aboard.
    If your sitting in the center of an 8' beam boat and say you weigh 200 lb. you will have a moment arm (leverage) of 4' * 200 lb. = 800 ft. lb.
    Let say the center of effort of your sail is 12' up. So 800 lb. / 12 = 67 lb. that and a little extra for the weight of the boat and your capsizing.
    For a small cat to go fast you need a good sail area / weight ratio and live ballast as far to windward as you can get.
    But I would prefer to sit in the middle of an under rigged cat, for leisurely sailing, vs a dinghy.

    Colin
    http://www.ww.xbug.ca
     
  14. quequen
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    quequen Senior Member

    Well, I wish someone could design a hobbie or a tornado for dissabled people. This is not the case, this device is not intended to fly a hull, just some fun and perhaps some equilibrium excercises, and capsize as part of that fun.
     

  15. PlaningWheel
    Joined: Nov 2010
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    PlaningWheel Junior Member

    Sorry queguen,

    Didn't understand the reason for the design.

    Maybe taking on water ballast and discharging it in each hull might be good.
    2 remote control scoops in each hull 1 pointing forward and the other pointing aft?
    The other advantage is if the wind really kicks up you can flood both hull tanks and sit very stable.

    And/or the ability to quickly reef your sail?

    When I was in my 20's I spent most of a year in a wheelchair and I have a small appreciation of how you need to improvise to make your situation better.
    I think the most important thing is that your brain works well. I would not want to end my days without at least one original thought.

    Yours,
    Colin
     
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